1. Field of the Invention
This invention relates to the processing of broad band signals and in particularly, fop use in active remote sensing sonars.
2. Discussion of Prior Art
Received broadband signals ape processed in several ways. One method of processing which is applied to broadband signals is known as highlight processing. This method is used for the detection of return signals from targets by detecting when the amplitude of the processed return signal exceeds a threshold level. One difficulty which arises with highlight processing is the ability to distinguish between the return signal from a target and reverberation echo. Reverberation is caused by a signal being reflected off natural objects such as the sea floor.
Broadband signals can also be processed to detect shadows. A shadow is created when the return signal is blocked by an object. The return signal which is usually used is the reverberation echo from a transmitted signal. Reverberation echo is generated across the whole range of distances from a receiver and therefore would be expected to be present for the whole duration of the return signal. However, when an object is located in the path of the reverberation echo, the reverberation echo is blocked by that object. Therefore, no reverberation echo would be present duping the period in which the reverberation echo from that direction would have been expected to be present. By detecting whether reverberation is present in a signal or not, it can be deduced whether there is an object present. Noise is also present throughout the whole duration of a return signal. A major problem, therefore, is being able to discriminate between the reverberation and noise.
At present the broad band signals are processed to detect the return signals in a single receive chain which may involve beam forming into a number of received beams.